In the oil and gas production and extraction industry, in order to access a hydrocarbon-bearing formation a wellbore may be drilled from surface, the wellbore typically then being lined with sections of tubing known as casing. In order to secure and support the casing in the wellbore, the casing may be cemented in place, a common cementing operation involving directing a cement slurry or the like through the tubing from surface, the cement exiting the casing at or towards its distal end to fill the annulus defined between the tubing and the wellbore.
During a cementing operation, a number of plugs or darts may be used prior to and subsequent to the passage of the cement. For example, a first dart or plug may be directed through the tubing in advance of the cement slurry, the first dart or plug operable to wipe or clean the inner bore of the tubing prior to passage of the cement slurry. A second plug or dart may be disposed behind the cement slurry, the second plug or dart wiping excess cement from the tubing before engaging the first dart or plug, the engagement causing a pressure event detectable at surface indicating that the cement operation has been completed.
Darts and plugs may take a variety of forms depending on the desired application and the dart or plug may, for example, be constructed from a number of sub-assemblies which are coupled together before being run downhole. While this may provide advantages in assembly and construction, the downhole environment presents a number of challenges for downhole equipment. For example, in addition to the high temperatures and pressures downhole, downhole equipment is typically subject to mechanical loads and vibration which can in some instances result in the dart or plug vibrating apart and causing an obstruction in the casing; requiring additional time and remedial operations to be carried out.